1. Field of the Invention
The present invention relates to a circuit breaker, and particularly, to a keylock device for a circuit breaker capable of preventing a main circuit from being arbitrarily closed again or tripped.
2. Background of the Invention
Generally, a circuit breaker is an apparatus for opening and closing an electric circuit so as to protect a load device and a circuit line from an accidental current due to an abnormal current such as short circuit, from a power plant or a substation to a user's electric equipments. This circuit breaker is classified into an alternating current (AC) circuit breaker and a direct current (DC) circuit breaker according to an application method to a circuit line, and is classified into a vacuum circuit breaker, a gas circuit breaker, etc. according to an extinguishing medium.
The circuit breaker is provided with a keylock device for mechanically locking the circuit breaker when the circuit breaker is in an ‘OFF’ state. The keylock device prevents the circuit breaker from being operated by any operator, by preventing the circuit breaker which is in an ‘OFF’ state from being in an ‘ON’ state unless an operator having a key releases a locked state. Accordingly, the keylock device for the circuit breaker has to have a structure to mechanically lock the circuit breaker with enhanced reliability and stability.
FIGS. 1 to 4 are views showing a keylock device for a circuit breaker in accordance with the conventional art.
As shown, the conventional circuit breaker comprises an opening lever 11 disposed to be rotatable between a closing position in which a fixed contact and a movable contact contact each other, and a breaking position in which the fixed contact and the movable contact are separated from each other; a trip arm 12 extendingly-formed at one side of the opening lever 11; a trip latch 13 disposed to contact or be separated from one side of the trip arm 12, and configured to allow or prevent rotation of the trip arm 12; a breaking spring (not shown) connected to one side of the opening lever 11 so as to be contracted or extended, and configured to apply an elastic force to the opening lever 11 such that the opening lever 11 rotates to a breaking position; a driving cam 14 rotatable centering around a rotation shaft disposed in parallel to a rotation shaft of the opening lever 11; a driving arm 15 rotatable by interworking with the driving cam 14, and having one end connected to the opening lever 11 by a plurality of links (not shown); a closing spring (not shown) connected to another end of the driving arm 15 so as to be contracted or extended, and configured to apply an elastic force to the driving arm 15 such that the driving arm 15 rotates to a closing position; and a closing lever 16 disposed at one side of the driving cam 14 so as to contact or be separated from the driving cam 14, and configured to allow or prevent rotation of the driving cam 14.
A roller 16a is coupled to the end of the closing lever 16 so as to roll-contact the driving cam 14, and a closing solenoid 17 configured to rotate the closing lever 16 is provided at one side of the closing lever 16.
A trip lever 18 configured to operate the trip latch 13 is rotatably installed at one side of the trip latch 13, and a trip solenoid 19 configured to rotate the trip lever 18 is provided at one side of the trip lever 18.
The closing lever 16 and the trip lever 18 are spacing from each other by a predetermined distance in upper and lower directions. And, a locking unit 20 configured to limit the operation of the closing lever 16 is installed between the closing lever 16 and the trip lever 18.
As shown in FIG. 2, the locking unit 20 consists of a key portion disposed in parallel to a rotation shaft of the opening lever 11, and moveable to a locking position or a releasing position, and a locking lever 22 rotatably coupled to the key portion 21, and configured to limit the operation of the closing lever 16 while rotating along a rotation direction of the key portion 21.
Unexplained reference numeral 23 denotes a key, and 24 denotes a locking pin.
The operation to open the circuit breaker by an operator will be explained as follows.
In order to check and repair a circuit line by an operator, power is supplied to the trip solenoid 19 such that the fixed contact and the movable contact of the circuit breaker are separated from each other. Once the trip solenoid 19 is supplied with power, the trip latch 13 rotates centering around a rotation shaft so as to be spacing from the end of the trip arm 12, and the opening lever 11 being provided with a tensile force rotates centering around a rotation shaft. Accordingly, the movable contact is separated from the fixed contact.
As shown in FIG. 3, if the operator inserts a key 23 into the key portion 21 thus to rotate the key into a locking position, the locking lever 22 rotates in a direction to restrict rotation of the closing lever 16. Here, the end of the trip latch 13 maintains a spacing state from the trip arm 12 by the locking lever 22. Accordingly, the operator withdraws the key 23 from the key portion 21 so as to prevent a main circuit from being closed by another operator.
Once the circuit line has been completely repaired and/or checked, as shown in FIG. 4, the operator inserts the key 23 into the key portion 21 thus to rotate the key 23 to a releasing position. As a result, the locking lever 22 is restored to the initial position by an elastic force of a trip latch spring (not shown). In this state, if power is supplied to the closing solenoid 17, the closing lever 16 rotates to be spacing from the driving cam 14, and the opening lever 11 rotates by an elastic force of the closing spring (not shown). Accordingly, the movable contact contacts the fixed contact, resulting in an ‘ON’ state of the mechanism.
However, the conventional circuit breaker may have the following problems.
When the current state of the locking unit is converted into a locked state from a released state in a state that the mechanism of the circuit breaker is in an ‘ON’ state, the mechanism is converted into an ‘OFF’ state. This may cause a main circuit of the circuit breaker to be broken against the operator's intention. More concretely, in order to prevent accidents due to an arbitrary operation, the operator has to withdraw the key after turning off the circuit breaker and converting the current state of the locking unit into a locked state. However, the conventional keylock device is configured to convert the current state of the locking unit into a locked state without turning off the circuit breaker. In this case, the circuit breaker may be turned off, and the main circuit may be suddenly broken. This undesirable breaking may cause accidents.